1. Field of the Invention
The invention relates to a control apparatus for a sealed fuel tank system which supplies vaporized fuel in a fuel tank to an engine.
2. Description of the Related Art
A sealed fuel tank system has a function for purging vaporized fuel (i.e., vapor) generated in a fuel tank without causing the vapor to leak to the atmosphere in a vehicle in which volatile fuel such as gasoline is supplied to the engine.
The sealed fuel tank system mainly includes a fuel tank which stores fuel in a sealed state, a vaporized fuel supply pipe which discharges (purges) vapor generated in the fuel tank to an intake pipe of an engine, and a control valve which opens and closes the vaporized fuel supply pipe.
In the sealed fuel tank system, when a pressure in the fuel tank (hereinafter, referred to as “tank pressure”) is equal to or higher than a target value, the control valve is maintained in an open state, whereby air containing the vapor is discharged from the fuel tank to the intake pipe using an intake vacuum pressure in the engine.
Meanwhile, in the aforementioned sealed fuel tank system, when an absolute value of the intake vacuum pressure in the engine which is applied to the fuel tank is low, the flow amount of the vapor discharged from the fuel tank to the intake pipe is reduced, and accordingly the pressure in the fuel tank may not be reduced to a target value.
An example of a conventional sealed fuel tank system is disclosed in Japanese Patent Laid-Open Publication No. 10-299582. In the sealed fuel tank system, a vacuum pressure chamber is provided in a vaporized fuel supply pipe, and vapor is purged through the vacuum pressure chamber when an absolute value of an intake vacuum pressure is low.
In this configuration, since the vacuum pressure chamber needs to be further provided in an existing sealed fuel tank system, the size of the system may become large, and the configuration of the system may become complicated.